The present invention relates to a control apparatus for an impact printer for use with various computer systems or word processors and provided with a set of interchageable type elements, which may be in the form of type wheels, for printing using different respective character fonts.
In an impact printer of the type described, printing operation is controlled based on various control data matching with the kind, font, size and other factors of type members, such as hammer pressure, amount of ribbon feed and amount of space, for the purpose of reproducing data which are readily identifiable. Since characters are available in upper and lower cases, hammering all the types with a same pressure would render the lower case letters denser than the upper case letters. In light of this, the hammer pressure is varied depending on the size of a character so that all the characters printed out will have a uniform density. Meanwhile, where use is made of a multistrike ribbon which can serve 3-5 times of repeated use throughout its length, some characters may each become uneven in density due to the repeated printing actions in each region of the ribbon. To ensure an even density over each character, the amount of ribbon feed is varied from one type to another. Also, should types be hammered at a predetermined intercharacter spacing, the reproduced characters would appear spaced different distances due to different widths of characters which might cause adjacent characters to overlap or be spaced too much. The intercharacter distance of reproduced data is usually controlled to predetermined one by varying the amount of space depending on the width of a type. It should be noted that the amount of space matching with the width of a specific type is referred to as a "proportional amount of space".
A known expedient for such a print control employs a read only memory or ROM which stores as code conversion tables the control data such as hammer pressures, amounts of ribbon feed and those of proportional spaces which correspond to type data using ASCII codes or JIS codes, for example, or type position data provided by converting the type data. During a print control operation, the code conversion tables are converted into hammer pressures, ribbon feeds and proportional spaces in response to input type data.
Meanwhile, some impact printers of the type described are furnished with a plurality of different kinds of interchangeable type wheels to win a wider range of applications. The type wheels may carry 88, 94, 96 and 128 type elements, respectively. Replacing the type wheel with another can change the kind of types, font, size etc.
In a printer with such interchangeable type wheels, the carriage is movable up and down relative to the printer body to facilitate the replacement of the type wheel which is loaded on the carriage. The carriage lacks grips for manipulation and usually raised with an upwardly extending hammer section held by hand, for instance. This is undesirable, however, because such a functional part of the carriage has been assembled by very delicate positioning. While this problem may be settled if suitable grips are mounted on the carriage independently of the other structural parts, such cannot be accomodated from the viewpoint of space requirement due to the highly compacted construction inherent in this type of products.
It is an object of the present invention to provide a control apparatus for a hammer type impact printer which permits the use of a plurality of different kinds of interchangeable type elements and promotes sure and easy replacement.
It is another object of the present invention to provide a control apparatus for a hammer type impact printer which when a type element is replaced with another, a print control can be effected merely by entering type data but not control data and, thereby, minimizes the intricacy of data processing procedure as well as the data transfer time to the printer.
It is another object of the present invention to provide a control apparatus for a hammer type impact printer which enhances the convenience of operation of the printer by providing a display of the kind of a specific type element to be replaced.
It is another object of the present invention to provide a control apparatus for a hammer type impact printer which allows one to grip the carriage for the replacement of a type element without requiring any additional space.
It is another object of the present invention to provide a generally improved control apparatus for a hammer type impact printer.
Other objects, together with the foregoing, are attained in the embodiments described in the following description and illustrated in the accompanying drawings.